Prior to the present invention, various manufacturing tools of plastic materials such as epoxy with fillers have been made to enable manufacturers to produce metal and plastics components in quantity and quality with economy and efficiency. Prior art U.S. Pat. No. 4,601,867 issued Jul. 22, 1986 to W. Martell and L. Weiss, assigned to the assignee of this invention and hereby incorporated by reference, discloses economical epoxy tooling cast directly from full size clay models for subsequent use in manufacturing high quality sheet metal stampings. By use of such epoxy tooling, expensive metal dies can be eliminated to reduce effort and costs for making such components. This prior art patent also discloses epoxy blow molds and injection molds for producing parts from plastics economically and efficiently.
The present invention is of the general category of that disclosed in U.S. Pat. No. 4,601,867, but further improves the tooling performance and durability by strengthening the internal properties of the epoxy body of the tooling. More particularly, longitudinally and laterally extending threaded rods are provided within the tooling and adjustable plates and washers mounted on the rods external to the tooling are used to encase and support the tooling to improve tool strength in areas of high tensile stress. By tightening nuts on the outer ends of the rods, compressive loads are induced into the tooling to match stress loads resulting from the stamping loads and shapes of the parts being processed. Because of the inherent nature of plastic tooling material to expand or contract with temperature change, the force of the compression plates or washers can be effectively adjusted by this invention to match the running temperature of the tool.
Preferably, epoxy tools of this invention for stamping parts from metal blanks are generally operated at room temperatures and the compression devices are torqued from a tool relaxed state to apply predetermined compression loads in areas of the tooling which will experience high tensile stress during stamping operation to prevent tool fracture and optimize tool life. Also, epoxy plastic molding tools of this invention are preferably operated at temperatures well above room temperature and have their compression devices torqued after tool heating and expansion to prevent cracking to optimize tool life. After use, the external compressive loads are removed from metal stamping and plastic molding epoxy tools so they will return to their normal unstressed state and not experience internal stress from the compression load devices of this invention.
These and other features, objects and advantages of this invention will become more apparent from the following detailed description and drawings, in which: